Comparison on Effects of ${\rm B}_{4}{\rm C}$, ${\rm Al}_{2}{\rm O}_{3}$, and SiC Doping on Performance of ${\rm MgB}_{2}$ Conductors

Several
${\rm MgB}_{2}$
monofilamentary samples are prepared to evaluate the effects that the doping compounds
${\rm B}_{4}{\rm C}$
,
${\rm Al}_{2}{\rm O}_{3}$
, and SiC have on critical current density
$(J_{\rm c})$
and the
$J_{\rm c}$
dependency of magnetic flux density
$(B)$
of the sample. All of the samples in this study have Nb sheaths and are manufactured using in situ precursor powders and the Powder-in-Tube fabrication method. The amounts of added impurities are 10 wt.% for
${\rm B}_{4}{\rm C}$
and
${\rm Al}_{2}{\rm O}_{3}$
, and 3, 10, and 20 wt.% for SiC. A reference sample without any doping is also prepared. All of the samples are heat treated between 650 and 800
$^{\circ}{\rm C}$
for 30 minutes. The transport
$J_{\rm c}(B)$
characteristics are measured at 4.2 K and the magnetic
$J_{\rm c}(B)$
behavior is obtained in varied temperatures up to 30 K. The changes in connectivity, or effective cross-section, are also evaluated by performing resistivity measurements on the samples after removal of the sheath. Furthermore, the pinning forces of the samples are evaluated from the magnetic measurements